Environmental Engineering Reference
In-Depth Information
fl ag so parents can keep their children indoors. The prevalence of asthma
has been increasing since the early 1980s, particularly among children,
but the reasons are uncertain. Certainly ozone, smog, and particulate
pollution can be suspected as complicit, but both of these villains have
been declining in abundance. Complicating the analysis is that asthma
has a genetic component. If one parent has asthma, chances are one in
three that each child will have asthma. If both parents have asthma, it
is 70 percent more likely that their children will have the disease.
Recent research has determined that ground-level ozone is associated
with changes in male sperm quality.
13
It is estimated that at least 2.1
million couples in the United States have diffi culty achieving pregnancy,
with male infertility responsible for 40 to 50 percent of infertility cases.
Hence, perhaps 1 million men may be able to attribute their diffi culty in
fertilizing their partner's eggs to ozone pollution. It is known that ozone
and its reaction products can cross the blood-gas barrier and enter the
bloodstream, and exposure to ozone can cause oxidative stress, which
has been shown to disrupt testicular and sperm function. As with
smoking, ozone exposure may trigger an infl ammatory reaction in the
male genital tract or the formation of circulating toxic species. Both
events could cause a decline in sperm concentration. No other pollutant
has been found to alter sperm quality or quantity.
Pregnant women exposed to the high concentrations of smog charac-
teristic of large cities have triple the risk of having a child with heart
malformations, the rate increasing from the normal 2 per 1,000 to 6 per
1,000.
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Sulfur
Two-thirds of the sulfur in America's air has been produced by human
activities, 80 to 85 percent of it from burning coal to generate electricity.
Coal contains 2 to 3 percent sulfur. The other 10 to 15 percent of atmo-
spheric sulfur comes from oil refi ning, commercial ships, and the smelting
of sulfi de ores. The sulfur is released from smokestacks as sulfur dioxide
gas (SO
2
), which reacts with the oxygen and water vapor in the air to
produce sulfuric acid (H
2
SO
4
), the major component of acid rain. Because
measurements by the Environmental Protection Agency (EPA) are taken
near the plant emitting the sulfur, smokestacks in factories are made to
be very tall, putting the gas and resulting acid high in the atmosphere,
where they are transported hundreds of miles before raining down.
Average acid rain is about ten times more acid than normal rain.
It is an enhancement of the natural and slight acidity of rainwater,
